1. Field of the Invention
The invention relates to a sliding-type tripod constant velocity joint.
2. Description of the Related Art
For example, Japanese Patent Application Publication No. 2003-65350 (JP-A-2003-65350) describes an existing sliding-type tripod constant velocity joint. In the sliding-type tripod constant velocity joint described in JP-A-2003-65350, rolling elements are supported by retainers in a state where each of the rolling elements is positioned with respect to intermediate members. With the above configuration, as power is transmitted, not only rolling resistance but also large resistance due to sliding occurs between the rolling elements and the intermediate members and between the rolling elements and raceway grooves.
Then, Japanese Patent No. 2763624, for example, describes a sliding-type tripod constant velocity joint in order to reduce the resistance. In the sliding-type tripod constant velocity joint described in Japanese Patent No. 2763624, needles are employed as rolling elements, and the rolling elements are supported by retainers so that they can circulate around corresponding intermediate members. This can greatly reduce the resistance due to sliding between the rolling elements and the intermediate members and between the rolling elements and the raceway grooves.
Incidentally, when a needle is used as a rolling element, a skew appears in the needle. A skew means a state where the central axis of a needle is inclined with respect to a direction in which the needle rolls. A skew in a needle generates a force in the axial direction on the needle.
Therefore, in the constant velocity joint described in Japanese Patent No. 2763624, each needle reciprocally moves in the axial direction of the needle with respect to the raceway groove of an outer ring due to a skew. Both ends of each needle in the axial direction are retained so that the needle is held by the retainer. Thus, as the needles move in the axial direction with respect to the raceway groove, the retainer that retains the needles also moves in the axial direction of the needles with respect to the raceway groove.
Here, in the above constant velocity joint, each retainer is fitted to the raceway groove of the outer ring. Therefore, when a skew appears in the needles, the retainer is clamped between the needles and the raceway groove. In order to ensure sufficient durability of the retainer even when the retainer is clamped, it is necessary to set a high bending rigidity for the retainer. For example, the retainer is thickened or the retainer is subjected to heat treatment. The above process causes an increase in the cost and weight of the retainer.